The background to the invention will now be set out with reference to the example applications of the authentication of security documents incorporating (typically printed on) a light permeable sheet of substrate material. However, the invention may be applied more generally to the authentication of other items, at least a portion of which has a thickness which is measurable using an optical thickness measurement.
Within this specification and the appended claims, by “security document(s)” we include documents of value, such as bank notes and bearer bonds; payment tokens, such as credit and debit cards and vouchers; certificates and identification documents, such as passports, driving licenses and identity cards. By the authentication of a security document, we refer to verification to a suitable level of certainty, which is typically less than 100%, that a security document originates from a prescribed or authorized source.
It is well known to provide security documents that include security elements, such as magnetic strips, special inks, print which is difficult to reproduce, optical features, such as holograms or diffraction gratings, and tamper-resistant electronic devices. Some security elements are overt to the human eye and some are covert, requiring knowledge of the element or special equipment to detect. Security documents are typically printed onto or embedded into a sheet of substrate material, such as a sheet of an appropriate paper, or plastics material, and it is known to provide apparatus to automatically authenticate documents by detecting security elements which have been introduced into or onto a sheet of substrate material.
However, standalone apparatus suitable for the authentication of security documents at points of sale is only in limited use at the present time. Points of sale may have a UV light source for detecting a fluorescent ink on a bank note, or a pen which does not mark authentic bank notes. These devices do not provide a high technical hurdle to counterfeiters. Points of sale may also have electronic apparatus which authenticates a credit or debit card using a tamper-resistant electronic circuit embedded in the card. However, this apparatus is complex and expensive, requires time to process and a telecommunications link to a remote server, and is not suitable for use in the authentication of bank notes during routine cash transactions.
More sophisticated apparatus for checking the authentication of bank notes is in common use by credit institutions and professional cash handlers for checking bank notes which are to be returned to circulation, but such apparatus is expensive, particularly as it is generally necessary to check for the presence of multiple security features to authenticate a bank note. Cash receiving machines have less sophisticated authentication apparatus as they have to be kept to a relatively low cost.
Some embodiments of the present invention aim to provide authentication apparatus and methods which can be implemented in a reasonably priced, reliable way such as to be suitable for use at a point of sale, or in a cash receiving machine. Some embodiments of the present invention aim to measure new or alternative properties of a security document, such as a bank note, to facilitate automatic authentication of security documents, or to present an additional hurdle to counterfeiters by providing one or more additional features which a counterfeit security document must have in order to be incorrectly determined to be authentic.
The invention makes use of known sheets of security document substrate which are permeable to electromagnetic radiation, for example, transparent in the visible region of the electromagnetic spectrum. It is known to create security documents, such as banknotes, by printing opaque inks onto sheets of transparent plastics substrate material, leaving a transparent window. The resulting window provides an overt security feature which is conspicuous to the human eye. It is known to print, etch or embed additional optical security features, such as optically variable devices formed by diffraction gratings, onto or into the resulting transparent windows, to provide additional overt security features. It is possible to provide automatic authentication apparatus which can determine authenticity from the presence or absence of these additional optical security features, but such apparatus is typically complex and expensive.
Some embodiments of the invention aim to use windows which have been left permeable to electromagnetic radiation (and typically transparent in the visible region of the electromagnetic spectrum) on security documents made from sheets of plastics substrate material which are permeable to electromagnetic radiation (and typically transparent in the visible region of the electromagnetic spectrum), to thereby provide one or more measurable characteristics which can be taken into account when determining whether a security document is authentic.
Some embodiments of the invention aim to provide sheets of substrate material for security documents which are adapted to facilitate authentication by the optical measurement of the thickness of one or more layers within the sheets of substrate material, as well as security documents include the said sheets of substrate material.
The invention also addresses the problem of authenticating products which may be counterfeited, such as alcoholic drinks, watches and other items of jewelry, perfumes, branded clothing, pharmaceuticals and cigarettes. It is well known to provide optically detectable security features, such as holograms, to be incorporated into the packaging of products, or into the products themselves. These optically detectable security features may be detected by the human eye, or by automatic authentication apparatus. However, features which are visible to the human eye can often be duplicated and the automatic authentication apparatus used to detect some known security features can be expensive.
Accordingly, some embodiments of the invention aim to provide alternative or improved methods and apparatus for authenticating products which may be counterfeited.
Furthermore, where overt optical security features are provided in or on products and security documents, they will be apparent to counterfeiters who can then address the problem of trying to reproduce the security feature. Some embodiments of the invention aim to authenticate items, such as products which may be counterfeited, or security documents, by measurement of an optical characteristic which is not readily apparent to the human eye, which may make it difficult for counterfeiters to determine which features are being verified during authentication.
According to a first aspect of the present invention there is provided authentication apparatus operable to determine the authenticity of an item responsive to the detection that a portion of the item has one or more predetermined characteristics, the said predetermined characteristics comprising either or both the thickness of the said portion of the item, and the thickness of one or more layers within the said portion of the item, determined by optically-based thickness measuring apparatus.
Thus, the authentication apparatus takes into account an inherent characteristic of the item (either or both the thickness of the said portion of the item and the thickness of one or more layers of the said portion of the item), rather than relying solely on the presence or absence of security features printed onto or incorporated into the item. This presents a technical difficulty to counterfeiters who, in order to cause the authentication apparatus to falsely authenticate a counterfeit document, would need to provide an item having a portion with the same thickness (where the thickness of the said portion of the item is taken into account) and a corresponding layer structure, (where the thickness of one or more layers of the said portion of the item is taken into account). Furthermore, this enables authentication apparatus to be provided which can authenticate a plurality of different items incorporating the same material, for example, security documents (e.g. banknotes of a variety of denominations or designs, or relating to different currencies) which are printed on substrate from the same (usually controlled) source, for example by different security printers, or products packaged in a sheet of material from the same source.
The item may be a product selected from a group comprising a container of alcoholic drink, an item of jewelry (e.g. a watch), a container of perfume, an item of clothing, a container of pharmaceuticals and container of cigarettes.
The said portion of the item may be an integral part of the product. However, typically the item is a packaged product, comprising both a product (such as a product selected from the group specified above) and packaging. In this case, the said portion of the item is typically the packaging, or a portion of the packaging, such as a sheet of electromagnetic radiation-permeable material.
Typically, the said portion of the item is a sheet of material. Thus, the invention extends to authentication apparatus operable to determine the authenticity of an item comprising a sheet of material responsive to the detection that the sheet of material has one or more predetermined characteristics, the said predetermined characteristics comprising either or both the thickness of the sheet of material, and the thickness of one or more layers within the sheet of material, determined by optically-based thickness measuring apparatus.
The item may be a security document comprising a sheet of substrate material, and said portion of the item may be the sheet of substrate material, or a portion of the sheet of substrate material. Accordingly, the invention extends to authentication apparatus operable to determine the authenticity of a security document comprising a substrate responsive to the detection that a security document has one or more predetermined characteristics, the said predetermined characteristics comprising either or both the thickness of the substrate of a security document, and the thickness of one or more layers of the substrate of a security document, determined by optically-based thickness measuring apparatus.
In order to minimize the complexity of the authentication apparatus, the predetermined characteristics may comprise only optically measurable characteristics of the sheet of material. However, the predetermined characteristics of an item which are taken into account when determining the authenticity of the item may further comprise predetermined characteristics of features printed onto, or introduced into, the sheet of material.
The predetermined characteristics may further comprise the birefringence of a sheet of material. This is advantageous as it is technically difficult to provide a sheet of material with no, or minimal birefringence, particularly a multi-layer sheet of plastics substrate material, suitable for use a security document substrate.
By using optically-based thickness determining apparatus, the thickness of a sheet of material, or one or more layers of a sheet of material, can be determined without destruction of the sheet of material. Typically, the apparatus is employed to authenticate items which comprise a sheet of material and one or more optical security features which are printed onto or incorporated into, the sheet of material.
The sheet of material should be permeable to electromagnetic radiation (such as visible light) and is preferably transparent. By transparent we refer to the property of allowing sufficient light in the visible region of the spectrum to be transmitted to enable an image to be clearly seen through the sheet of material and include sheets of material which fulfill this criteria but are tinted or partially reflective. However, the sheet of material is typically substantially clear. The sheet of material may transmit at least 90% of visible light which is incident normal to the surface.
The authentication apparatus may be used to authenticate security documents which are opaque across the majority (typically the substantial majority) of their surface area, with only a minority of the security document being light permeable. For example, the security documents may be opaque except for one or more transparent windows. The security documents typically comprise a light permeable, and preferably transparent, sheet of substrate material, the majority of which is covered with an opaque material.
The said characteristics may include the presence of an optically permeable region of a security document (for example, a window which has been left transparent) and the authentication apparatus may be adapted to determine whether there is a region of a received security document which is permeable to electromagnetic radiation of a predetermined range of frequencies (e.g. transparent). The predetermined range of frequencies typically include some or all of the visible region of the electromagnetic spectrum, and optionally some of the near infra-red region of the electromagnetic spectrum. The authentication apparatus may determine whether there is a region of a received security document which is permeable to electromagnetic radiation of a predetermined range of frequencies by determining whether there is both a region which is permeable to electromagnetic radiation of a predetermined range of frequencies and a region which is opaque to electromagnetic radiation of the predetermined range of frequencies. Whether or not there is a region which is optically permeable may be determined by determining whether a thickness measurement can be made. A source of electromagnetic radiation and a detector of electromagnetic radiation may be provided to determine whether or not there is a region which is not permeable to electromagnetic radiation of the predetermined range of frequencies.
The one or more predetermined characteristics may comprise or consist of the overall thickness of a sheet of material. The one or more predetermined characteristics may comprise or consist of the overall thickness of a sheet of material, except for a surface coating layer on one or both opposite faces of the sheet of material. The one or more predetermined characteristics may comprise or consist of the overall thickness of the sheet of material plus an electromagnetic radiation permeable coating on one or both faces of the sheet of material. The latter two options are especially relevant where the item is a security document and the sheet of material is a sheet of substrate material.
The one or more predetermined characteristics may comprise or consist of the thickness of an individual layer within a portion of an item (such as a sheet of material) having a plurality of layers. The said individual layer may be located between at least one layer on each side of the said individual layer. This presents a technical challenge to a counterfeiter who is then required to prepare a portion of an item (such as a sheet of material) which includes a layer of defined thickness within the body of an item. The predetermined characteristics may comprise or consist of the thickness of two or more said individual layers within a portion of an item having a plurality of layers (such as a multi-laminate sheet of material).
The one or more predetermined characteristics may comprise or consist of the combined thickness of a group of adjacent layers within a portion of an item (such as a sheet of material) having both the group of adjacent layers and at least one further layer. The combined thickness of a group of adjacent layers may, for example, be measured using interferometric methods based on the interference between electromagnetic radiation reflected from interfaces at either end of the group of adjacent layers. The group of adjacent layers may be located within a sheet of material having at least one further layer on each side (normal to the plane of the substrate) of the group of adjacent layers. The predetermined characteristics may comprise or consist of the thickness of two or more said individual layers within a portion of an item having a plurality of layers, such as the thickness of two or more said individual layers within a sheet of multi-laminate material.
The predetermined characteristics may comprise or consist of the thicknesses of each of a plurality of layers, or groups of adjacent layers (which groups may overlap) which generates a measurable signal, due to the reflection of electromagnetic radiation, in excess of a threshold value.
Preferably, the thickness measuring apparatus comprises a source of electromagnetic radiation, for example a source of white light, and a detector of electromagnetic radiation, for example a spectrometer, for detecting electromagnetic radiation from the source of electromagnetic radiation which has interacted with an electromagnetic radiation permeable portion of the item. This enables thickness measurements to be carried out, as electromagnetic radiation which is incident on the surfaces of an item, such as an item comprising a sheet of material, and the boundaries between layers within a sheet of material, is reflected, and may also have its polarity altered as a result. Typically, the source of electromagnetic radiation generates electromagnetic radiation in the visible part of the spectrum, and a detector of electromagnetic radiation detects electromagnetic radiation in the visible part of the spectrum. The source, and detector, may also emit and detect, respectively, light in the near infra-red part of the spectrum.
Preferably, the detector of electromagnetic radiation is configured to measure electromagnetic radiation which has been reflected from a region of the item which is permeable to electromagnetic radiation of a predetermined range of frequencies. However, where the thickness of a sheet of material, or one or more layers within a sheet of material, is measured the detector of electromagnetic radiation may be arranged on an opposite side of a received sheet of material to the source of electromagnetic radiation, so as to detect electromagnetic radiation which has been transmitted through the sheet of material. Generally, fewer reflections are required to produce an interference pattern at the detector when reflected electromagnetic radiation is analyzed.
Preferably, the source of electromagnetic radiation is operable to direct electromagnetic radiation of a predetermined range of wavelengths onto the item, and the detector is operable to measure electromagnetic radiation of a predetermined range of frequencies. Typically, the source of electromagnetic radiation will be operable to emit broadband electromagnetic radiation (e.g. white light). Typically also, the detector will be operable to measure the intensity of electromagnetic radiation at a range of wavelengths simultaneously. For example, the detector may be a spectrometer. However, the light source may be operable to generate electromagnetic radiation at a range of wavelengths at different times, for example to sweep the wavelength of generated electromagnetic radiation from one wavelength value to another wavelength value. In this case, the detector may be wavelength independent. Similarly, the detector could in principle be operable to detect electromagnetic radiation of a range of different wavelengths at different times.
Accordingly, the optically-based thickness measuring apparatus typically functions as a broadband (e.g. white) light interferometer. An advantage of using broadband light interferometry is that it is possible to measure the thickness of more than one layer, or groups of adjacent layers, within an item simultaneously, by looking for interference caused by reflection from different pairs of interfaces between adjacent layers. However, alternative optically-based thickness measuring apparatus may be employed based on techniques known to those skilled in the art for measuring the thickness of films, such as ellipsometry or spectral reflectance, or by using a prism coupler, or by measuring the net amount of absorption of electromagnetic radiation (e.g. electromagnetic radiation in the infra-red part of the spectrum) or beta radiation through the item.
The predetermined characteristics may include the lack of layers, or groups of layers, having thicknesses which would not be present in an authentic document. The predetermined characteristics may comprise whether the layer structure within a sheet of material is symmetrical. This may be determined from the lack of intensity peaks which should not be present, and the relative intensity of peaks. Where two separate layers of the same thickness are present in a symmetrical sheet of material, a more intense peak corresponding to that thickness should be present than when only one layer of that thickness is present.
The predetermined characteristics may include characteristics related to the relative intensity of reflections from one or more interfaces on the surface of an item, or between layers within the item. This provides an additional distinguishing characteristic to use in authentication. The relative intensity of reflections may be determined from the relative intensity of interference between electromagnetic radiation reflected from different pairs of interfaces, for example, using broadband light interferometry.
The apparatus is typically adapted (e.g. pre-programmed) to recognise predetermined characteristics of a portion of an item with specific properties, such as a specific thickness, the presence of layers having specific thicknesses, and/or a specific birefringence. Thus, the apparatus may be adapted to recognize a specific portion of an item, such as a sheet of material. The apparatus may be adapted to recognize a sheet of material made from biaxially-oriented polypropylene (BOPP). Preferably, the apparatus is adapted to recognize a multi-layer sheet of material, all or most of which is made from BOPP. The apparatus may be adapted to authenticate security documents according to the fourth aspect of the invention, discussed below.
The invention also extends in a second aspect of the present invention to a method of determining the authenticity of an item wherein the method comprises detecting whether a portion of the item has one or more predetermined characteristics, the said predetermined characteristics comprising either or both the thickness of the said portion of the item, and the thickness of one or more layers within the said portion of the item, determined by optically-based thickness measuring apparatus.
The item may be a product selected from a group comprising a container of alcoholic drink, an item of jewelry (e.g. a watch), a container of perfume, an item of clothing, a container of pharmaceuticals and container of cigarettes.
The said portion of the item may be an integral part of the product. However, typically the item is a packaged product, comprising both a product (such as a product selected from the group specified above) and packaging. In this case, the said portion of the item is typically the packaging, or a portion of the packaging, such as a sheet of material which is permeable to electromagnetic radiation.
Typically, the said portion of the item is a sheet of material. Thus, the invention extends to a method of authenticating an item comprising a sheet of material, the method comprising detecting whether the sheet of material has one or more predetermined characteristics, the said predetermined characteristics comprising either or both the thickness of the sheet of material, and the thickness of one or more layers within the sheet of material, determined by optically-based thickness measuring apparatus.
The item may be a security document comprising a sheet of substrate material, and said portion of the item may be the sheet of substrate material, or a portion of the sheet of substrate material. Accordingly, the invention extends to a method of authenticating a security document comprising a sheet of substrate material, the method comprising detecting whether the sheet of substrate material has one or more predetermined characteristics, the said predetermined characteristics comprising either or both the thickness of the sheet of substrate material, and the thickness of one or more layers within the sheet of substrate material, determined by optically-based thickness measuring apparatus.
The authenticity of the item is preferably determined using authentication apparatus according to the first aspect of the invention. Optional features of the authentication apparatus, method of operation of the authentication apparatus and the items which are authenticated by the method of the second aspect correspond to those discussed in relation to the first aspect of the invention.
According to a third aspect of the present invention, there is provided a sheet of substrate material for a printed security document, the sheet of substrate material comprising a plurality of layers of material which is permeable to electromagnetic radiation (and typically transparent in the visible region of the electromagnetic spectrum), wherein two adjacent layers have significantly different refractive indices. One said layer may comprise a polymer and the second said layer may comprise the same polymer with the addition of an additive which affects (typically increases) the refractive index of the polymer, such as titanium dioxide. The sheet of substrate material may comprise first, second and third layers, the first and third layers having substantially the same refractive index as each other, second layer being located intermediate and in contact with the first and third layers and having a higher refractive index than the first and third layers to reflect incident electromagnetic radiation. In this case, the first and third layers are preferably substantially thicker than the second layer. Thus, the first and third layers can be selected to obtain desired physical characteristics and the second layer can be selected to enhance reflection and improve measurements of the thickness of the first, second or third layers, or one or more groups of adjacent layers including the first, second or third layers.
The first and third layers may comprise biaxially-oriented polypropylene (BOPP). The second layer may also function as an adhesive to join the first and third layers.
The invention also extends in a fourth aspect to a security document, such as a document of value, comprising a sheet of substrate material according to the third aspect of the invention, the surface of which is predominantly printed with ink which is opaque in the visible region of the spectrum except for a window which is permeable to a visible light where the thickness of one or more layers including the first layer, the second layer or, where present, the third layer, can be measured.